The update that came into effect earlier this month, outlined that Trade Me may use some personal information of members in its marketing.
It covered members who had elected to opt out from their personal information being used for marketing or advertising purposes.
Commissioner John Edwards said it contained some ambiguities and he wanted to make sure it had been handled responsibly and transparently.
He also wanted to find out what the affected users thought of the changes.
"Potentially an organisation can collect a whole lot of information on one basis and set of understandings, and then unilaterally and arbitrarily change those rules.
"I want to ensure that where that happens we have a good look at it, and satisfy ourselves that it's done according to the law."
Edwards said he wanted to know if the changes applied to information that was supplied to the organisation on the understanding that it would not be used for particular purposes.
He said it was important to look at these things in today's digital environment.
Edwards said it was the first time he had notified an inquiry of this type.
"But when I look around the world at different business models, such as any of the big platforms, as their business has grown and changed, their privacy policies change incrementally and they can end up quite a long way from where they started.
"That means the individual might end up in a situation where their relationship with the organisation is quite different from the one they were signing up with from the outset," Edwards said.
He said he had not pre-determined any outcomes, but from early engagements with Trade Me it appeared there had been some ambiguity in the wording of some of the documents, which meant there could be misunderstandings at play
"But I want to understand and I think it's important that organisations know from time to time that they will be asked to explain, and possibly be held to account."
Edwards was inviting feedback from Trade Me members who may have been affected by the update, as well as any general comments on the changes from members of the public.
That included whether members felt they understood the scope and limits of the marketing and advertising opt-outs Trade Me offered, whether they had expressed concerns to Trade Me about the way in which they were notified, and any other comments that members wanted to make about the update and changes to internal procedures.
Feedback is open until 10 February.